1. Field of the Invention
The present invention relates to ceramics, and particularly to a method of laser surface treating pre-prepared zirconia surfaces, including yttria-supported zirconia, in order to harden the surfaces.
2. Description of the Related Art
Carbonitriding is a metallurgical surface modification technique that is used to increase the surface hardness of a metal, thereby reducing wear. During the process, atoms of carbon and nitrogen diffuse interstitially into the metal, creating barriers to slip, and increasing the hardness and modulus near the surface. Carbonitriding is often applied to inexpensive, easily machined low-carbon steel to impart the surface properties of more expensive and difficult to work grades of steel. Surface hardness of carbo-nitrided parts ranges from 55 to 62 HRC. An economical carbonitriding process applicable to zirconia might also address surface hardness issues for zirconia.
Laminates or composites produced by zirconia and yttria powders contain fine pores, which affect the structural homogeneity of the laminates and composites. Zirconia (ZrO2) is usually doped with small fraction (2-3%) of yttria (Y2O3) to conserve ZrO2 cubic (c-ZrO2) or tetragonal (t-ZrO2) high temperature phases down to room temperature. Surface treatment of yttria-stabilized tetragonal zirconia enhances the surface properties, such as corrosion and wear resistance, and improves the structural integrity at the surface through re-melting. The use of high energy lasers for surface treatment of such materials would offer considerable advantages, including local treatment, short processing time, and precise operation. Laser nitrogen gas-assisted processing of the surface could provide for the formation of zirconia nitride (ZrN) in the surface region. This would further improve the wear resistance of the surface, which would make it possible to use the treated surface in the cutting tool industry and hardness required other applications. Injecting particles during laser gas assisted processing modifies the surface chemistry and microstructure at the surface. The formation of zirconium carbide (ZrC) at the surface is desirable, since it is non-oxide ceramic with mixed ionic and metallic bonding, as well as high hardness.
Thus, a method of laser surface treating pre-prepared zirconia surfaces solving the aforementioned problems is desired.